Thermionic tube test apparatus



May 7,1946. J. B. CRAWLEY ,8

THERMION IC TUBE TEST APPARATUS Filed Feb. 24, 1944 as 41 a \ou'raur 27"ii g 30 arn/am WWW/M7085 VOZT/fifii Juventor attorney Patented May 7,1946 l THERMIONIC TUBE 'rns'r ArrAnA'rUs James B. Crawley, Edenton, N.C., assignor to Radio Corporation of America, a corporation of DelawareApplication February 24,1944, Serial No. 523,736

2 Claims.

This invention relates generally to thermionic tube test apparatus andmore particularly. to an improved test set formeasuring the operatingcharacteristics of thermionic tubes in combination with thermionic tubegenerating and voltage measuring apparatus.

Many tubes employed in modern radio receivers and transmitters includeone or more control electrodes in addition to the cathode and anodeelectrodes. Such multi-electrode thermionic tubes may be employed toamplify or to generate radio frequency voltages. In order properly totest tubes of these types,.a true measure of tube emciency only isobtainable by testing the tube in a circuit comparable to the circuit inwhich it is to be regularly utilized. Since test sets ordinarily arerequired to be portable in nature, it obviously would be impossible toinclude all customary receiver and transmitter circuit elements fortest--: ing a large variety of thermionic discharge tubes...

Because of simplicity and low cost, the emission type tube tester hasbeen most generally used. In this type of tester the anode and allcontrol electrodes are connected together, and a voltage of the order of30 volts is applied between the oathode and the parallel-connectedelectrodes. A

paratus such; for example, as in lining-up" a conventional radioreceiver. In addition, the vacuum tube voltmeter or other measuringapparatus may be connected to external equipment for conventionalvoltage measurements. The customary tapped transformers and resistorsemployed in the mutual conductance type testers are included to providedesired operating voltages for the several tube electrodes. 3

Among the objects of the invention are to provide an improved method ofand means for testing thermionic discharge tubes. Another object of theinvention is to provide an improved method of and means for testingthermionic tube circuits and apparatus. An additional object of the in--vention is to provide improved thermionic tube apparatus comprisingmeans for testing a, thermionic tube as an oscillation generator, meansfor measuring alternatively the generated grid bias voltage or thegenerated high frequency voltage developed by such oscillations, meansfor providing a. source of high frequency test oscillations and meansfor providing a thermionic tube meascur'rent meter connected in serieswith the voltage v source provides a comparative indication of the tubecathode emission. A tapped transformer is employed to supply the correctcathode voltage for the particular tube under test. Such emissiontesters do not provide satisfactory test information concerning theamplifying or generating characteristics of multi-electrode tubes.

Dynamic mutual conductance testers wherein the various tube electrodesare connected to proper operating potentials, and wherein the amplifiedoutput current responsive to a fixed input signalis measured, provide atubeefliciency test for one predetermined value of control grid voltage.However, a completely satisfactory test requires that the control gridbias voltage be varied over a reasonable range. I

The instant invention contemplates a tube tester wherein a plurality ofdifferent circuit elements may be connected selectively to the anode,cathode and control electrode terminals of the test socket to providethermionic tube oscillating circuits of predetermined proportions andresonant frequencies. A thermionic tube voltmeter, or other indicator,may be connected to the control electrode of the tube under test tomeasure the grid bias'voltage developed in response to the generatedoscillations. The measuring instrument alternatively may be connected tothe anode portion of the oscillating circuit to measure the voltageamplitude of the generated high frequency oscillations. Connections areprovided for employing the oscillations thus generated as a testgenerator source for energizing external apuring'circuit for externalmeasurements.

The invention will be described in greater detail by reference to theaccompanying drawing of which the single figure is a schematic circuitdiagram of a preferred embodiment thereof.

Referring to the drawing, the tube tester includes a test socket (orsockets) l for the diiierent types of thermionic tubes to be tested. Theheater terminals 2, 3 are connected through a first switch Sl to atapped secondary winding 4 of a heater transformer 5, the primarywinding 6 of which is connected to a source of altemating potential. Thecathode terminal 1 of the test socket I is connected to the movablecontact 8 of a second switch 9. One fixed contact of the second switchii is connected through a first inductor Hi to ground. A second fixedcontact of the second switch 9 is connected directly to ground. A thirdfixed contact oi. the second switch 9 is connected to an intermediatepoint I l-on' an oscillator inductor l2, one end terminal of which isgrounded. A fixed, or variable, tuning capacitor I3 is connected inparallel with the oscillator inductor [2. The ungrounded en'd terminalsof the oscillater inductor l2 and tuning capacitor [3 are connected tothe common terminals of a plurality of difi'erent-sized grid capacitorsi4, l5, ii. The

remaining terminals of'the grid capacitors ll, l5.

is connected through a smoothing resistor 26 to a fixed contactof afifth switch 21 which is connected through a bypass capacitor 28 toground. The smoothing resistor 26 and bypass capacitor 28 comprise an RCfilter for the measuring circuit of the oscillator grid voltage to bedescribed hereinafter.

The anode terminal 29 of the test socket I is connected to the movablevcontact 30 of a sixth switch 3|, through a feed-back capacitor 32 to theungrounded common terminals of the oscillator inductor l2 and tuningcapacitor I3, and through an output capacitor 33 to a high potentialoscillator output terminal 34. The remaining output terminal 35 isgrounded.

The fixed contacts of the sixth switch 3'! are connected, respectively,through a feedback resistor 36; and through oppositely-phased feedbackreactors 31, 38, coupled to the oscillator reactor l2; to an adjustabletap 33 upon a first voltage divider 40. The first voltage divider 40 isconnected across a source of relatively high D.-C. voltage, such, forexample, as a conventional high voltage rectifier circuit, not shown;

The anode terminal 29 of the test socket I also is connected through asecond output capacitor 4| to a second fixed contact of the fifth switch21. An additional fixed contact of the fifth switch 21 is connected toan external terminal for applying voltage from any source of externalvoltage to be measured. a

The movable contact 42 of the fifth switch 21 is connected to one end ofa second voltage divider 43. The remaining terminal of the voltagedivider 43 is grounded. A movable. tap 44 on the second voltage divider43 is connected to the control electrode of a vacuum tube voltmeter tube45. The anode of the voltmeter tube 45 is connected to the highpotential terminal of the first voltage divider 40 to provide anodevoltage therefor. The cathode of the vacuum tube voltmeter tube 45 isconnected, through a cathode resistor 46 and an indicating current meter41, to ground. The indicating meter 41 preferably should be calibratedin terms of the voltage applied across the second voltage divider 43.

In operation, the operating potentials for the heater and anodeelectrodes of the tube under test in the test socket I are adjusted bymeans of the first switch SI and the movable tap 39 on the first voltagedivider 40, respectively. The desired value of the grid capacitor forthe tube under test is selected by adjusting the third switch l1.Similarly, the value of grid leak for the tube under test is selected byadjusting the fourth switch 2|.

Adjustment of the second switch 9 and the sixth switch 3| provides aconvenient method of connecting the oscillation circuit elements to thetube socket to provide the desired type of oscillation circuit for thetube under test.

Actuation of the fifth switch 21 selectively connects the input of thevacuum tube voltmeter either to (1) the grid electrode of the tube undertest, (2) the oscillator anode circuit or (3) the terminal for a sourceof external voltage to be measured.

When the fifth switch movable contact is connected to the grid electrodeterminal IQ of the test socket l, the vacuum tube voltmeter indicator 41provides an indication of the grid bias.

voltage developed in the tube under test, in re-' selected oscillatorcircuit connections as deter-.

mined by the positions of the second, third, fourth and sixth switches9, [1, 2| and 3|, respectively.

Similarly, when the fifth switch 21 is connected to the oscillator anodecircuit through the second output capacitor 4 I, the vacuum tubevoltmeter indicator 41 provides an indication of the magnitude ofthe-generated high frequency output voltages. If desired, a separatediode detector may be substituted for the vacuum tube voltmeter formeasuring the magnitude of the generated oscillations.

As explained heretofore, the high frequency oscillations applied to theoscillator output terminals 34, 35 maybe employed for testing externalapparatus such, for example, as for lining-up a conventional radioreceiver.

It should be understood that the various switching arrangements may bepredetermined with respect to the desired eiliciency tests on particulartypes of thermionic tubes, and that the indicating meter 41 may becalibrated in any manner most convenient for indicating particular tubeoperating characteristics. The various switches may be of either therotary or push-button types common to thermionic tube test sets;

Thus the invention disclosed comprises a thermionic tube test setwherein tubes under test are operated as oscillation generators in anypredetermined type of oscillation circuit, wherein the grid potentialdeveloped in response to said oscillations or the oscillation voltagemagnitude may be selectively measured, and wherein the generatedoscillations may be employed for driv ing external apparatus. I claim asmy invention:

1. Test apparatus for thermionic discharge tubes including a socket forreceiving a tube to be tested, means connected to the terminals of saidsocket providing a selectively adjustable oscillation circuit for saidtube, separate adjustable means connected to said socket for providingadjustable grid bias, cathode and anode voltages for said tube forderiving sustained oscillations therefrom, a thermionic tube voltmeter,and means for selectively connecting said voltmeter to said socket andto said oscillation circuit for providing indications of grid biasvoltage and oscillation voltage respectively to provide therebycooperative indications of the operating efficiency of said tube.

2. Test apparatus for thermionic discharge tubes including a socket forreceiving a tube to be tested, means connected to the terminals of saidsocket providing a selectively adjustable oscillation circuit for saidtube, separate adjustable resistive means connected to said socket forpro-

